In the cleaning industry there is a need to handle a wide range of liquid chemical, including alkalis, detergents, bleaches, acids and the like. These chemicals have a variety of viscosities and concentrations requiring dilution, usually with water, before use. Moreover, these are harsh, possibly hazardous chemicals requiring special handling, including the need to flush out remnants of the previous chemical from common feed pipes. Many other industries present combinations of such problems.
In use the specific proportions of the various chemicals delivered must be controlled for efficiency, performance, repeatability and low cost.
Known systems pumped the chemical directly into the process equipment for use with peristaltic pumps. The peristaltic pumps are used as the chemicals are viscous. Wear and aging problems with the peristaltic pumps lead to inaccuracies in volume delivered and metering systems were developed. But the flow meters cannot be used with viscous fluids.
To overcome this viscous problem the chemicals are diluted with water enough to allow the flow meters to function properly, but the amount (volume) of chemical added is the critical parameter to be controlled not a diluted chemical. One metering system is in use wherein the dilution is compensated. In this metering system a water supply is pumped into a dilution manifold where a number of different chemicals may be pumped into the flow stream. The chemicals are diluted enough to allow the flow meters to function and the diluted flow is directed from the dilution manifold through a totalizing flow meter to the processing equipment. A system controller, by turning on or off the various chemical pumps, and by measuring the total flow rate, determines the amount of chemicals supplied to the process machines.
In a typical operation, only the water pump is turned on and the flow meter records a given flow rate. When a chemical pump is turned on, the flow meter records a different (higher) flow rate, with the difference accepted to be due to the added chemical volume. By recording the flow rates the controller can determine what volume of each chemical is being delivered.
The above described flow metering system has some limitations. The water pump must deliver a fixed volume and pressure that remains constant when the pumps for the chemicals to be added are activated. If the flow rate of the water pump changes errors are introduced. Control of this pump is done by the system controller turning it on or off. The system controller also turns on or off the chemical pumps and the proportions delivered are determined by programming a differential volume into the system controller. For example, to deliver a given volume of a chemical, the water pump is turned on and the flow rate measured; then a chemical pump is turned on and the flow meter responds with a higher flow rate--the difference, due to the chemical being pumped, is measured until the desired amount of chemical has been added. In this system peristaltic type pumps are still used because the chemicals are viscous and must be injected into the water flow stream at a pressure great enough to overcome the water pressure involved. With such equipment, controlled as described, the actual mixture delivered may vary by considerable amounts. If the chemical feed lines to or from the chemical pumps are partly empty, say due to settling, the volume of chemical delivered will be less than if the feed lines were filled. In addition the peristaltic pumps, wherein rollers squeeze resilient tubes, cause wear and distortions on the tubes and rollers resulting in differences in the rate of delivery as the pumps and tubes wear. As previously described, the system is referenced to the water pump flow rate being constant, but if the water pump changes its flow rate as the chemicals are pumped, say due to high back pressures, or the mixing of the chemical and water is not directly additive, errors are introduced.
Other disadvantages stem from the use of the peristaltic pumps. These pumps are expensive (ten such pumps in a single system are common) and often in need of service to repair worn rollers and replace the feed tubes. The replacement and cleaning of such pumps is labor intensive, and care must be taken when handling harsh chemicals often found in the cleaning industry and in like industries.
The result of these prior art system limitations is that non-uniform mixtures are often obtained and this results, ultimately, in non-uniform cleaning performance or other performance degradation associated with failure to deliver prescribed mixture proportions.
An object of this invention is to produce a system where volumes of fluid chemical additives are reliably achieved with improved safety, accuracy and precision.
It is another object of this invention to eliminate the peristaltic pumps, thereby decreasing cost, and further increasing reliability and decreasing service requirements.
It is a further object of this invention to provide a system with fewer service requirements and long life.
Another object of this invention is to provide a system that may control many processing machines.
Another object of this invention is to tailor the hydraulic flow path to the specific liquids being delivered in order to compensate for different viscosities and flow requirements.